Here is a nice presentation of the evidence:

Frank J. Swetz (The Pennsylvania State University), "Mathematical Treasure: The Cambodian Zero," Convergence (October 2015) - See more at: http://www.maa.org/press/periodicals/convergence/mathematical-treasure-the-cambodian-zero#sthash.8llx0OXX.dpuf
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--
Professor Dominik Wujastyk
​,​

Singhmar Chair in Classical Indian Society and Polity
​,​

University of Alberta, Canada
​.​

South Asia at the U of A:
 
​sas.ualberta.ca​
​​